Detector for hidden metal



May 23, 19x33.

G. E. BLINN DETECTOR FOR HIDDEN METAL Filed May 1:5, 1951 INVENTOR BY en/12u, mm1/L1.'

ATTORNEYS Patented May 23, 1933 L for-electrical service of diderent kinds.

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umn-Eu STATES PATENT oFFlcE GLENN E. Buma, or NEW Yoan, N. Y., AssIcNon To Beaver s. WALKER, or Ammonia rmmsnvam DETECTUR FOB HIDDEN METAL Appxmtiqn met ny 1s,

type described which is off simple, compact construction, easil moved about andv of special utility in discoverin such concealed objects as the ducts and oor boxes of an under-door duct system.

At ythe present time, it is the customary practice to install elaborate duct systems 1n the floors-ot modern concrete buildin, these ducts serving lor the distribution l I n such systems, the ducts are buried beneath the door to a substantial distance and in some systems the location oi the ducts can only be ascertained by reference to the building plans. lin other systems such as that described in llllatent lilo. ltdfl, issued duly ld, i926, the ducts are provided with outlets on a uniiorrn spacing, which outlets extend up toward and are intended to terminate hush with the iloor surlace. llt occasionally happens that the tops el the outlets ot the system ol "the patent are covered by a thin hlm ol licor material and usually, even though the outlets terminate dash vvith the door, they are concealed bythe door covering oi linoleurn or the lilac. .its a con--y sequence, it is sometimes diwcult, even with the patented system, to determine the loca-l tion ol the ducts Without relierring to the plans and melting' measurements trom partitions, columns, or the like.

The present invention is accordingly d1- rectedA to the provision of a simple, inexpensive mechanism, electrically operated, vby which -it is possible to determine accuratel the location of concealed metal objects suc as underdoor ducts above referred to.

The new device involves producing an al ternating magnetic field, either of the continuous Wave or oscillating types, .and then detectin any distortion of the field vvhlch results rom metal objects within the field. In'therdevice, the field is set, up by a coil carrying electric current and 'a second coil is disposedo at right angles to the dlrectlon of flux through the rst coil, so that little Wiring 1931. Serial No. 537,032.

or no current flows through the second coil by induction in the absence of disturbing influences. However, if the first coil is moved into the vicinity of a metal object and under such circumstances that the object caus'es a distortion of the flux in the field produced by that coil, current is induced to flow through the second coil, and the flow of current is detected by suitable means, such as a telephone receiver or galvanomcter. AThe magnitude oi the signal given by the receiver or galvanometer increases as the coils approach the concealed o object, and by moving the apparatus in the vicinity ot the object, the location oli the cti latter may be determined vvithgreat accuracy.

For a better understanding ci the inven tion, reference may be had to the accompanying drawing, in which' Fig. l is a plan vievv ci an embodiment ci the device, showing the Wiring;

F ig. 2 is a side vien7 oil the device shoufing only the position oi the coils Fig.. 3 is a Wiring dia ram oi the device.

its illustrated in the ravving, the device includes a primary coil lll mounted in a casing ll in such a position that the anis thereot is parallel to the bottom ot' the cas ing. The coil is supplied `with current iront an outside source ol current through a conductor cable Ml, and one lead vvire ld inside the bon connects the cable to one terminal ol the coil and lead Wires l'l and l@ connect the cable to the other coil terminal through a buzzer 19, a condenser 20 being connected across the contacts ol the buzzer in the usual manner. With this construction eitherv alternating or direct current may be supplied to the coil, as ioreaample from the suply wiring ol the building lor lill to be described later. The terminals of the coil 21 are connected to terminal posts 23 and 24 to which head phones 25 located outside of the casing may be. connected by suitable conductors.

In the operation of the device, the latter is connected to a source of current and a magnetic field established by coil 10. The operator then puts on the head phones and moves the device over the area where the metal objects are mown to be concealed. When the movement of the device causes a part of the flux in the iield produced by coil 10 to be intercepted by the concealed object, the field is distorted, and current induced inthe secondary coil 21. This causes a signal in the phones and by moving the casing about until the signal reaches its maximum intensity, the location of the object is determined.l` A pencil, crayon, or the like is then passed through the casing through openings 12 to mark the spot on the surface nearest the object.

1 claim:

A device for detecting hidden'metal, comprising a casing having a fiat bottom surface, a coil within said casing having its axis normal to the bottom surface of said casing, said coil having an open core and said casing having openings in the walls thereof in ali nment with said open core, a second coil within the casing lying at one side of said first coil and with its axis substantially arallel to the surface to be tested, an means for detecting current flowing through said ,first coil.

ln testimony whereof I affix my si ature.'

GLENN E. B INN. 

